Synthesis and characterization of hydrophilicity-controlled poly(arylene ether sulfone) copolymers with phenolphthalein-based carboxylic acid groups for separation membrane applications

Hydrophilicity-controlled poly(arylene ether sulfone) copolymers with phenolphthalein-based carboxylic acid groups (PES-COOH-X) were synthesized via direct copolymerization by adjusting the feed molar ratio. The chemical structures of the obtained copolymers were confirmed by 1H nuclear magnetic resonance (NMR) spectroscopy. The copolymers showed good solubility in common aprotic solvents and exhibited excellent mechanical properties. The water contact angles of the obtained copolymers could be reduced by approximately 52% from 92.1° to 44.2° with increasing content of phenolphthalein-derived monomer, 2-[bis(4-hydroxyphenyl)methyl] benzoic acid (PPH-COOH), in the feed molar ratio. A series of PES-COOH-X membranes was prepared via a conventional immersion precipitation phase inversion method. The effects of the monomer feed molar ratio on the morphology, hydrophilicity, pure water flux, and water uptake of the prepared membranes were investigated. The results showed that the pure water flux of the PES-COOH-X membranes was significantly enhanced by almost a factor of two as compared to the pristine PES membrane. From the water contact angle data, it was identified that the hydrophilicity of the membranes was increased rapidly with increasing PPH-COOH content in the membranes. These hydrophilicity-controlled poly(arylene ether sulfone) copolymers may be considered as good candidates for separation membrane materials.